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Sept 12, 11%39. M. KNOLL ELECTRICAL LENS Filed July 26, 1934 @(HUEEEDEQ LAB a 5 MEL (1iDD:f:

INVENTOR newnaunnunnonnn MXA OAL BY l ATTORNEY Patented Sept. 12, 1939 uNiTsnf-sr ELECTRICAL LENS k 1 Max Knoll, Berlin, Germany, .assignor to Telefunken Gesellschaft'fiir Dralitlose Telegraphic m. b.H., Berlin, Ge Germany many, a corporation of Application July 26, 193 4,2 Serial No. 737,021

In Germany July 31, 1933 4 Claims. (01; 250-162) The present invention relates to electron tubes, principally of the cathode ray type, and is directed particularly to a method and means of focusing a developed cathode ray at any selected 5 point.

The electrical lenses heretofore described for accomplishing the focusing of'a cathode ray usually do not consist of more than three electrodes. This number of electrodes has heretofore [0 appeared to be suificient insofar as it was believed to be possible to influence in an adequate degree the course of the equi-potential surfaces corresponding to the front and rear surface of the optical lens by correspondingly choosing the 5 diameter of the electrodes and the distance between the electrodes and insofar as only cathode ray beams of comparatively small cross sections were used which correspond with the central rays of an optical lens.

, The present invention is, however, based upon the teaching that an electrical lens which can be understood to be chromatically corrected, and a lens which can be considered as spherically corrected, cannot be obtained by the steps hitherto 5 taken.

to exist if a lens reproduces cathode rays of various hardness in the same point. The rays of various hardness may at the same time be present in the source of electrons in the same manner as :0 ,a polychromatic light source radiates light of a different wave length. The rays of various hardness may, however, also have their cause in the voltage fluctuations of the current source serving for the anode potentials, or in the residual alter- 5 nating voltage of, for instance, a battery eliminator which is not entirely perfect. Under spherical correction there is understood in an electrical lens the possibility of concentration of comparatively large beam cross sections which 0 corresponds to the faultless reproduction of also the border rays and not only the central rays of an optical lens.

Various modes of execution of the invention are schematically shown by the several figures of the accompanying drawing wherein:

Fig. 1 shows conventionally a cathode ray tube having a plurality of separated focusing electrodes therein and wherein all other portions of the tube and its associated electrodes are shown in schematic form only;

Fig. 2 shows in its several portions the course of the equi-potential surfaces and field curvature resulting from connecting the electrodes of Fig. 1

5 to different points on a resistor element through A chromatical correction is understood 1 which the potential course is such that the oathode ray is caused to converge;

Fig. shows in its several portions features similar to Fig. 2 except that the cathode ray is caused to diverge; and

Fig. 4 shows a modification of the form of resistance element of Figs. 1, 2 and 3.

Referring now to the drawing, and first to Fig. 1, numerals ID to l9 represent ring-shaped electrodes of large diameter as compared with the cross section of the cathode ray beam originating from the cathode l within the tube envelope 3. The electrodes H) to l9 are connected to a potentiometer resistance 20 to which voltages are supplied as shown by Figs. 2 and 3. By suitably selecting the connection points and hence the voltage for each of the electrodes Ill to ill, which may, for instance, be ascertained by way of experiment, the chromatic and spherical correction can be accomplished in the mentioned sense. That this can actually be accomplished will be recognized in considering those means by which the chromatic and spherical correction in an optical lens is carried out. In an optical lens the faults of the picture are eliminated namely by correspondingly selecting the radii of curvature and the exponents of refraction of the individual lenses of which the lens is composed. To the radii of curvature of the individual lenses of an optical objective there corresponds in an electrical lens the equi-potential surfaces of the electrical field produced by the electrode potentials. To the exponent of refraction of the individual lenses there corresponds the electron velocity at the passage through the respective equi-potential surface. Thus, the chromatic and spherical correction in an electrical lens can be achieved by a corresponding selection of the electrode potentials.

By referring to Fig. 2, the course of the equipotential surfaces and curvature resulting therefrom of the electron rays will be elucidated. The electrodes as in Fig. 1 are again designated by H to H! and a potentiometer resistance along which the electrode voltages will be tapped is designated by 20. To this resistance an auxiliary current may be supplied at a tap point P1 between the end points, and voltages may be taken therefrom at the two end points P2. The connection points of the electrodes on the resistance 20 are so chosen that along the axis of all electrodes a potential course exists as shown by the bottom sketch in Fig. 2. The electrical field lines extending at right angles to the equi-potential surfaces are shown at two places only in Fig.2

and are indicated therein by arrows, whereby the direction of the arrow is chosen in the same sense in which an acceleration of the electrons occurs.

The direct results of the arrangement of Fig. 2 are that to a divergent cathode ray beam entering at left into the electrodes, a reduction of divergence is imparted. The electrical field intensity possesses a component at the place of entrance which is at right angles to the electron path, and thus causes a bending of each individual course of flight of the electrons. In passing through the electrodes arranged at the right side of the arrangement, thus for instance, in passing through the electrode l9 there likewise exists a component of the electrical field intensity at right angles to the direction of flight of the electrons, so that also here the divergence of the cathode ray beam will be diminished.

The mentioned components of the electrical field intensity are directed towards the common axis of all electrodes at the left as well as at the right end of the electrode arrangement, which in View of Fig. 3 to be immediately described, is of importance.

The arrangement according to Fig. 3 differs from that of Fig. 2 only in that the point P1 of the potentiometer resistance 28 is connected to the negative pole of an auxiliary current source, while the two ends P2 are placed at the positive pole. The auxiliary current through resistance 20 thus has in Fig. 3 the opposite direction from that in Fig. 2. Although this has no influence upon the picture of the equi-potential surfaces between the electrodes and thus does also not influence the picture of the electrical field lines, however, it reverses the direction of the electrical field lines so that, as will be immediately explained the functioning alters basically. The directions of the arrows are therefore shown opposite in Fig. 3 from those in Fig. 2. If into electrode it in Fig. 3 a divergent cathode ray beam enters from the left, the component of the electrical field intensity acts at right angles to the course of flights of the electrons likewise in the sense of a curving of the path. This component, however, is, contrary to the conditions as existing in Fig. 2, directed away from the axis common to all electrodes. The divergence of the cathode ray beam therefore will be increased. The same is true for the curving of the path caused at the right end of the electrodes. The arrangement according to Fig. 3 thus acts increasing upon the divergence of the cathode ray beam, so that an effect is produced similar to that produced by a dispersion lens upon a beam of light rays.

It must be expressly pointed out that the auxiliary current may be supplied to the potentiometer 20 of Fig. 2 as well as of Fig. 3, also at more than one point P1.

By a modified embodiment the invention, as shown in Fig. 4, consists of a current conducting resistance 2| in the form of a helix of more than three windings. The voltage drop through a single winding hereby corresponds to the voltage of two successive electrodes in Fig. 1. The choice of the connection points at the resistance 26 corresponds in the arrangement according to Fig. 4 to a variable dimensioning of the resistance of each single winding. The helix in the same manner as the potentiometer 20 in Fig. 2 and Fig. 3 has one or several points P1.

The described examples of embodiments show that simply by the use of a larger number of electrodes or helical windings respectively, which however are all identical, thus affording a very simple construction and that furthermore by the selection of the voltages effective therebetween, a corrected electrical lens can be produced. Furthermore, for the first time an electrical lens has been produced by the means indicated, which With the means hitherto known has not been possible at all.

The invention besides being applicable to electrical lenses for electron rays can also be applied to such for ion rays.

Having thus described the invention, what I claim is:

l. A cathode ray tube comprising an electron source, a viewing screen adapted to become luminous upon impact of developed electrons thereupon, a plurality of substantially identical annular cylindrical electrode elements in excess of three, said electrode elements being positioned intermediate to said source and said screen and adapted to have predetermined voltages appliec thereto for producing electrical fields of different positive and negative curvature to vary the degree of convergence or divergence of the cleveloped electron beam, and means for positioning the controlled electron beam to various areas of the viewing screen.

2. A cathode ray tube comprising an electron source, a viewing screen adapted to become luminous upon impact of developed electrons thereupon, a plurality of substantially identical annular cylindrical electrode elements in excess of three surrounding the stream of electrons, said electrode elements being positioned intermediate to said source and said screen and adapted to have predetermined voltages applied thereto for producing electrical fields of different positive and negative curvature to Vary the degree of convergence or divergence of the developed electron beam, and means for positioning the controlled electron beam to various areas of the viewing screen.

3. Electrode structure for focusing an electrically developed ray beam which comprises, means for causing the developed electron beam to traverse predetermined elemental sections of a predetermined surface, and means for producing intermediate the source at which the electron beam is developed and the area upon which it impinges a plurality of electrical fields in excess of three, each of said fields being developed successively at distances more remote from the source, said fields varying progressively and uniformly through opposite signs of convergence, and directing the developed electron beam successively through said fields.

4. A cathode ray tube comprising an electron source, a viewing screen adapted to become luminous upon impact of the developed electrons thereupon, a plurality of spirally arranged conducting wrappings positioned intermediate to said source and screen, said wrappings being adapted to have applied thereto electrical energy of predetermined value and adapted when so energized to develop a spherically and chromatically corrected electrical lens focusing on the viewing screen.

MAX KNOLL. 

